Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens, and more particularly, to a zoom lens suited for use in a broadcasting television camera, a cinema camera, a video camera, a digital still camera, a monitoring camera, and a silver-halide film camera.
Description of the Related Art
In recent years, a zoom lens having a wide angle of view, a high zoom ratio, and high optical performance is desired for use in an image pickup apparatus, e.g., a television camera, a cinema camera, a film camera, a silver-halide film camera, a digital camera, or a video camera. In particular, an image pickup device, e.g., a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), which is used in a television or cinema camera serving as a professional moving image pickup system, has a substantially uniform resolution over the entire image pickup range. Therefore, a zoom lens using the image pickup device is required to have a substantially uniform resolution from the center to the periphery of the screen. There are also needs for reductions in size and weight for an image pickup mode that places emphasis on mobility and operability. Meanwhile, an exchangeable lens for use in a television or cinema camera needs to secure a satisfactorily long back focus.
As a zoom lens having a wide angle of view and a high zoom ratio, there is known a positive lead type zoom lens in which a first lens unit having a positive refractive power and a second lens unit having a negative refractive power for zooming are arranged in order from an object side. For example, in Japanese Patent Application Laid-Open No. H06-242378, there is described a zoom lens having a zooming ratio of about 8 and an angle of view of about 87 degrees at a wide angle end, and including, on the image side of a second lens unit, a third lens unit for correcting an image plane variation accompanying zooming, and a stop configured not to move during zooming. Moreover, in Japanese Patent Application Laid-Open No. 2014-63026, there is described a zoom lens having a zooming ratio of about 11 and an angle of view of about 76 degrees at a wide angle end, and including, between a second lens unit and a lens unit on an image side of the second lens unit, a stop configured to move during zooming.
As a zoom lens having a wide angle of view and a high zooming ratio, there is known a positive lead type five-unit zoom lens including five lens units, of which a lens unit having a positive refractive power is arranged closest to an object side, and in which the following three movable lens units: a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power are configured to vary magnification and to correct an image plane variation accompanying the zooming (Japanese Patent Application Laid-Open No. H07-248449 and Japanese Patent Application Laid-Open No. 2009-128491).
In Japanese Patent Application Laid-Open No. H07-248449, there is disclosed a zoom lens having a zooming ratio of about 17× and a photographing angle of view of about 70 degrees at a wide angle end. In Japanese Patent Application Laid-Open No. 2009-128491, there is disclosed a zoom lens having a zooming ratio of about 54× and an angle of view of about 60 degrees at a wide angle end.
The positive lead type zoom lens having the above-mentioned structure is relatively easy to realize a wide angle of view, but in order to realize both high optical performance and downsizing, it is important to appropriately set refractive power arrangement of the lenses. In particular, an off axial ray passes through the first lens unit, which is closest to the object side, at a position farthest from the optical axis. Therefore, in order to realize both the optical performance and the downsizing, it is important to appropriately set a position of the stop in the optical system, shares of zooming among lens units configured to move during zooming, and a refractive power and a configuration of the first lens unit.
In the zoom lens described in Japanese Patent Application Laid-Open No. H06-242378, the stop is arranged on the image side of the second and third lens units, which are responsible for zooming. Therefore, the stop is away from the first lens unit, resulting in increases in lens diameter and number of lenses of the first lens unit. Moreover, in the zoom lens described in Japanese Patent Application Laid-Open No. 2014-63026, the stop, which is configured to move during zooming, is arranged between the second lens unit and the third lens unit in a manner that is advantageous in downsizing the first lens unit. However, the refractive power of the first lens unit is small, and a paraxial arrangement appropriate for realizing an even wider angle of view and downsizing is not obtained.
The positive lead type zoom lens disclosed in each of Japanese Patent Application Laid-Open No. H07-248449 and Japanese Patent Application Laid-Open No. 2009-128491 is relatively easy to realize a wide angle of view and a high zooming ratio, but in order to realize both a wide angle of view and downsizing, it is important to appropriately set refractive power arrangement of the lenses. In particular, an off axial ray passes through the first lens unit, which is closest to the object side, at a position farthest from the optical axis, and hence the first lens unit tends to become larger than other lens units. Therefore, it is important to appropriately set refractive powers of the first lens unit and the second lens unit. Moreover, appropriate setting of refractive powers and movement loci of the lens units configured to move during zooming may bring the off axial ray closer to the optical axis on the wide angle side of the first lens unit, and reduce an aberration variation during zooming, with the result that both the optical performance and the downsizing may be realized. In the zoom lens disclosed in each of Japanese Patent Application Laid-Open No. H07-248449 and Japanese Patent Application Laid-Open No. 2009-128491, of the second to fourth lens units, which are responsible for zooming, the second lens unit is configured to move monotonously from the object side to the image side, and the third and fourth lens units are configured to move substantially monotonously from the image side to the object side. The third lens unit and the fourth lens unit have relatively close movement loci, and hence are suitable for increasing the zooming ratio. However, the refractive powers of the respective lens units tend to become larger, and a manufacturing error tends to affect the optical performance.